The invention relates to a signal processor for a multiple beam receiving antenna array, such as may be used in radar applications.
In a pulsed surveillance Radar system designed to give, for example, elevation information, a transmitting antenna is pulsed with a radio frequency f.sub.c, the duration and repetition rate of the pulses being determined by the normal constraints of range resolution and maximum unambiguous range for the system. The transmitting antenna is so designed that each transmitted pulse floods the whole sector to be covered. Reflection from a target anywhere in the sector is received by a linear array of antenna elements. Considering a given phase front for the received signals, it is clear that the signals received by the antenna elements will have an incremental phase difference, which is constant between successive antenna elements of the array. The amount of this phase difference is related in a known way to the angle of the target with respect to the axis (boresite) of the linear array. The received signals become outputs from the antenna elements and are then fed to a signal processor in which there is derived a signal which contains a component bearing a direct relationship to the angle of the target.
The concept of synthetic aperture radar is well known, and technical outgrowths of that concept have continued. Aperture Signal Processing is a term which involves the element by element processing of received signals in a planar phased array, for example. The technical literature, for example the text "Radar Handbook" by Merrill I. Skolnik (McGraw-Hill Book Co. 1970), provides a background in this regard.
The so-called Doppler Guidance systems (simulated Doppler by commutation of the elements of the transmitting array) provies a conceptual step in the development of Aperture Signal Processing Radar Systems. The patent literature is extensive in that connection, and the journal "Electrical Communication" published by International Telephone and Telegraph Corporation, Vol. 46, No. 4 (1971), pp 253-270 summarizes the technique in an article entitled "Doppler Scanning Guidance System". Although that system is basically a one way technique (for ground transmission and air borne signal processing for angle determination) it nevertheless contributed to the development of Aperture Signal Processing.
The manner in which the Aperture (array) Signal Processing art is advanced by the present invention will be understood as this description proceeds.